Caching in mobile networks is a relatively well known technology. Caching utilizes the fact that a large percentage of Internet traffic is repetitive, and eliminates the need for repeating content all the way from its origin, which may save time and resources. The main principle of caching is that copies of frequently requested content in e.g. the Internet is moved from the origin and stored closer to the mobile users, for example in different parts of the RAN (Radio Access Network), in the CN (Core Network) or just above the CN.
The main benefits that can be achieved with caching in mobile networks are:                The cost of transport in the mobile network above the cache may be decreased, since the cached information, in principle, is only transferred once in the transmission links above the cache. i.e. from the origin to the cache.        The QoE (Quality of Experience) for the mobile end-users may be improved, e.g. by reduced delays. The reduced lower delays are achieved as the cached information can be returned faster to the mobile users from the cache, as compared to if the information would have been retrieved all the way from the original location.        There will be opportunities for the operators to provide new services, such as content hosting and storage/backup. For example, a mobile operator can sign agreements with one or more content providers, according to which the mobile operator ensures that the content from these specific content providers will be delivered in a better way to the mobile users in the mobile operator's network.        
Consequently, caching can be used for media distribution towards mobile users as an alternative to retrieving downloadable media from a more remote media server or from other users, by that the media is retrieved from the cache. FIG. 1 shows how media information from a media server is pushed into a cache in a mobile network, and how the mobile users receive the information directly from the cache instead of from the media server. It is also worth mentioning that caching can be used for almost any internet content and that FIG. 1 is just an example based on media services.
One important component of caching is packet inspection, which is performed in order to identify if a content request is related to information which is already stored in the cache or if the content can be saved in the cache when it is being forwarded to the client requesting the content. Packet inspection may be seen as a first natural step towards full Deep Packet Inspection (DPI) in the RAN. The use of DPI in the RAN enables collection of information related to the content of the packets, which may be used for so-called learning user profiling or subscriber profiling over longer periods of time and between different sessions. The RAN becomes aware of the different services used by the end users by using DPI in the RAN, and this is the definition of the Service Aware RAN. One important aspect of the user profiling is to store information about the different services used by the different end users.
FIG. 4 shows an illustrative example of Service Aware RAN for E-UTRAN/LTE, WCDMA/HSPA and GSM/GPRS/EDGE. In the figure a Service Aware RAN function is shown as a common component for all three RATs. It can be based on PS user plane made to traverse via this function and then, for example, identifying the different services based on packet inspection/DPI
An important component for the user profiling is the access to a permanent UE identifier, which enables tracking of the activities of a certain user/UE. In this document, the term permanent UE identifier is used for both mobile subscription identifiers for the subscription used on a UE and for UE identifiers. Examples of such permanent UE identifiers are e.g. IMSI (International Mobile Subscriber Identity), IMEI (International Mobile Equipment Identity), IMEISV (International Mobile station Equipment Identity and Software Version Number) and MSISDN (Mobile Subscriber Integrated Services Digital Network Number). The permanent UE identifier is needed as it, in combination with packet inspection/DPI, enables building of databases over for example:                user service pattern—e.g. what is the user doing?        user geographic locations—e.g. where is the user doing whatever she/he is doing?        user specific time patterns—e.g. when is the user going to do it?        
It may be desirable to perform such user profiling at all times when a user is active in a communication network. For example, it may be desirable to perform user profiling of a user also when she/he moves between systems using different Radio Access Technologies (RATs), such as e.g. GSM/GPRS/EDGE, WCDMA/HSPA and LTE. FIG. 2 shows an exemplary network with three different RATs.
As previously stated, a UE user (SIM card) is uniquely identified by the IMSI number. In a scalable, learning, adaptive and Service Aware RAN, the possibility to track performance over time related to a specific user requires that a long term unique identifier is available in the RAN.
In a short time perspective, introducing or moving e.g. Legal Intercept (LI) and charging functionality in or into SA-RAN, would require that the IMSI is detected in the RAN. The motivator for moving down LI from the core network to RAN would be that operators may have the core network nodes in one country and the RAN in another country, and that LI has to be performed within the country in which the LI is ordered.
The LI function identifies a UE to be intercepted with an IMSI. The user activities in terms of downloads and internet accesses need to be reported to the LI organization. In a scenario where a cache is located in a RAN and the LI function is interfaced via the core network (as of today) the content which is played out from the cache need to be uniquely associated with/connected to an intercepted UE, in order to enable reporting of the correct information to the LI function.
Another situation where a permanent UE identifier may be desired could be when there is a need for developing RAN policies, or a set of rules, in RAN that is applicable to a unique UE. The development of such policies or rules would require that IMSI is detected in the RAN. An example of such a rule could be that a certain UE is excluded or barred from using a RAN cache or other RAN unique services. Another example of a RAN policy could be that a certain user should have his/her content accelerated via services located in a RAN cloud.
A further reason for desiring access to a permanent UE identifier in a RAN is subscriber profiling, as mentioned above, to enhance how the services are delivered in RAN. One example situation where a user could benefit from user profiling is e.g. when every week day, the user takes a bus to work, every day at approximately the same time of day, the bus drives in to a long tunnel with unfavorable radio conditions, and the user is thus out of radio coverage for 2 minutes. Geographic information identifying the cell with the tunnel and an intelligent selection of content, e.g. the news paper that is read every day or the remaining part of the film that is streamed, could be used to trigger a pre-download of content to the subscriber, and thus anticipate and minimize the impact of the loss of coverage in the tunnel.
The different permanent UE identifiers are defined in 3GPP TS 23.003. The definition of IMSI is also illustrated in FIG. 3. The IMEISV, IMEI and the MSISDN will not be further described in this disclosure.
As illustrated in FIG. 3, the IMSI is composed of three parts:                Mobile Country Code (MCC) consisting of three digits. The MCC identifies uniquely the country of the mobile subscriber.        Mobile Network Code (MNC) consisting of two or three digits. The MNC identifies the home PLMN (Public Land Mobile Network) of the mobile subscriber. The length of the MNC (two or three digits) depends on the value of the MCC.        Mobile Subscriber Identification Number (MSIN) identifying the mobile subscriber within a PLMN.                    The National Mobile Subscriber Identity (NMSI) consists of the MNC and the MSIN.                        
However, there is at least one problem which needs to be resolved in order to achieve the services described above for all RATs, and that is the fact that there is no permanent UE identifier available in certain RANs such as e.g. in E-UTRAN/LTE. Instead, a temporary identity, such as e.g. S-TMSI (System Architecture Evolution-Temporary Mobile Station Identity), is used when the UE communicates with the network. Further, the temporary identity gets re-assigned frequently.
The reason for not allowing permanent UE identifiers in certain RANs is that it has been considered as a risk for personal integrity to have identifiable information of user activities in base stations, such as eNBs, since the security of these nodes cannot be guaranteed. For example, base stations can be placed in insecure environments or sites. Further, base stations sites are normally not manned with operator personnel and therefore the threat for someone breaking into a base station is higher, as compared to for example an RNC (Radio Network Controller) site for WCDMA (where IMSI is available). Further, the so-called femto base station or Home eNB (HeNB) in LTE (Long Term Evolution) has the same architecture as a macro eNB, and if IMSI would be made available in eNBs, then it would also be available in HeNBs that can be placed almost anywhere.
If e.g. IMSI would be made available in base stations, such as eNBs or HeNBs, and someone would illegitimately break into such a base station, this someone would possibly be able to access information on exactly which terminals that were attached to the base station and to track these terminals and the actions of their users.
Thus, in the LTE case, the different permanent UE identifiers like IMSI, IMEI, IMEISV and MSISDN are only known in the core network, i.e. in the EPC (Evolved Packet Core) (and not in the access network). In the LTE RAN, different temporary identifiers are used. For WCDMA/HSPA and GSM/GPRS/EDGE, IMSI is already made available in BSC/RNC.
One solution to the above described problem would be to modify the LTE core network, EPC, e.g. the MME, to support delivery of permanent UE identifiers to eNBs in E-UTRAN/LTE. Such an approach is described in the document WO2011/019085. However, such modifying of the LTE core network is not desired, e.g. due to the above reasons related to user identity confidentiality in the base stations.